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E:W
Microemulsion
C:O
FIGure 9.4
Four-component system: Oil (O)-Water (W)-Emulsifier (E)-Cosurfactant (S)
(ratio of O:S versus S:W).
potential at the surface of oil droplets will be dependent on the concentration of ions
in the surrounding water phase.
The state of stability under these conditions can be qualitatively described as
follows. As two oil droplets approach each other, the negative charge gives rise to
a repulsive effect (Figure 7.4). The repulsion will take place within the electrical
double-layer (EDL) region. It can thus be seen that the magnitude of double-layer
distance will decrease if the concentration of ions in the water phase increases. This
is because the electrical double layer region decreases. However, in all such cases in
which two bodies come closer, there exists two different kinds of forces that must
be considered:
Total force = repulsion forces + attraction forces
The nature of the total force thus determines whether
The two bodies will stay apart
The two bodies will merge and form a conglomerate
This is a very simplified picture, but a more detailed analysis will be given else-
where. The attraction force arises from van der Waals forces. The kinetic movement
will finally determine whether the total force can maintain contact.
9.2.4 o
r I e n TaT I o n
of f
m
of l e c u l e S
a T
o
I l
-W
a T e r
I
n T e r f a c e S
At this stage in the literature, there is no method available by which one can directly
determine the orientation of molecules of liquids at interfaces. Molecules are situ-
ated at interfaces (e.g., air-liquid, liquid-liquid, and solid-liquid) under asymmetric
forces. Recent studies have been carried out to obtain information about molecular
orientation from surface tension studies of fluids (Birdi, 1997). It has been concluded
that interfacial water molecules, in the presence of charged amphiphiles, are in a
tetrahedral arrangement similar to the structure of ice. Extensive studies of alkanes
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